Paper having special strength characteristics



Sept. 7, 1965 w. A. SELKE PAPER HAVING SPECIAL STRENGTH CHARACTERISTICS 2 Sheets-Sheet 1 Filed April 30, 1965 l f m 6' INVENTOR' IV/ZL/AM A. 642%! ArroiZiV United States Patent 3,205,124 PAPER HAVING SPECIAL STRENGTH CHARACTERISTICS William A. Selke, Stockbridge, Mass., assignor to Kimberly-Clark Corporation, Neenah, Wis., a corporation of Delaware Filed Apr. 30, 1965, 'Ser. No. 454,244 5 Claims. (Cl. 162- 136) This application for patent is a continuation-in-part of applicants copending application, Serial No. 270,724, filed April 4, 1963.

This invention relates generally to paper and its manufacture, and has particular reference to paper in which the fibres are disposed in a predetermined manner to make the paper useful to produce tubes having optimum hoop strength.

In the process of manufacturing paper on a Fourdrinier wire or its equivalent, the fibres dispose themselves at portion to cos 0 and the transverse component is proportional to sin 6 where 0 is the angle between the fibre and the machine direction.

The summation of components in the machine direction:

is usually greater than the summation of components in the transverse direction:

2 sin 0 because of the tendency of the web movement to cause a majority of the fibres to lie at angles 0 less than 45. As a result, paper is usually stronger in the machine direction than in any other. This is often a disadvantage, and to avoid this, papers have been made in which the fibres are more or less equally divided between those which lie at angles less than 45 to the machine direction, and those which lie at angles greater than 45. Such paper is sometimes referred to as being square. The mean value of all the angles 0 is 45, and the paper manifests a strength which is about as great in the transverse direction as along the longitudinal axis of the web. I

Neither ordinary paper nor ,square paper is ideally suitable to form a tube (with its axis in the direction of the paper web) because for such a purpose the paper should have more strength in the transverse direction than in the longitudinal direction. In fact, since the vhoop stress on a tube'is twice the longitudinal stress, it follows that if a continuous paper web is to be made into a tube or series of tubes, with the tube axis parallel to the longitudinal axis of the web, the paper shouldf'tfor optimum effect) have a strength in the transverse direction which is exactly twice that in the machine direction.

It is a primary object of the present invention to provide such a paper. More particularly, it is an object of the invention to produce a paper on a Fourdrinier machine, by essentially conventional commercial paper-making techniques, in which a predetermined preponderance of the fibres of which the paper is made are disposed at such angles, greater than 45 to the machine direction, that the strength of the resultantpaper in the transversedirecdifference between ice tion is twice its strength in the machine direction. That is to say, the ratio 2 sin 0 2 cos 0 has a value of 2, where 6 is the angle between each fibre and the machine direction.

In attaining this objective, it has been found insufficient merely to provide for a majority of the fibres to lie at angles -0 greater than 45. Two requirements must be met: first, the mean value of 0 must be at least are tan 2 (about 63); for if the mean value is less than this the desired strength characteristics of the paper would be impossible to achieve even if all the fibres were (theoretically) aligned at an angle 0 less than 63, since the component in the transverse direction would be less than twice the component in the machine direction. Secondly, the number of fibres lying at angles 0 greater than 45 must be large enough-and just large en-oughto impart the value of 2 to the ratio (1). Even if the mean value of 0 is greater than about 63 the desired strength characteristics cannot be attained unless the magnitude of the 2 sin 0 and 2 cos 0 is of adequate and proper size.

Paper made in accordance with this invention may be used to form sausage casings or the like, but the applicability of the invention is not restricted to any such purpose.

One way of producing a paper having the qualities and capabilities of the kind referred to is illustrated in the accompanying drawings, in which FIG. 1 is a schematic plan view of a paper-making machine adapted to produce paper according to the present invention;

FIG. 2 is a vertical cross-sectional view taken on line 2-2 of FIG. 1;

FIG. 3 is a fragmentary perspective view of a continuous web of paper produced by a machine of the type shown in FIGS. 1 and 2;

FIGS. 4, 5 and 6 are diagrams showing various possible fibre dispositions;

FIGS. 7 and 8 are diagrams depicting the strength characteristics of ordinary and square papers, respectively;

FIGS. 9, 10 and 11 are strength diagrams of papers in which maximum strengths are in a direction forming an angle of about 63 to the machine direction;

' machine direction; and

FIG. 14 is a fragmentary perspective view of a tube formed from the web of FIG. 3.

The fibres of which the paper is made are suspended in a slurry in accordance with usual practice. If the paper is to be porous, the fibres are unbeaten, or at most very lightly beaten. FIGS. 1 and 2 show schematically part of an inclined wire Fourdrinier machine in which the forming wire, during its travel, becomes immersed in the paper stock. The head box 11 is filled with paper stock 10 through an opening 12. An endless mesh forming wire 13 is trained about the breast roller 14 and the idler rollers 15, and passes through the paper stock in the direction of the arrow in FIG. 2. As the wire 13 continues to move, the paper fibres 18 are deposited on it whereby a continuous web of paper 19 is formed. During the course of web formation in this manner, fibres dispose themselves at all angles to the machine direction. Those depicted at 18 are of course only those which orient themselves in the general direction shown, andare not intendedto-be representative of all fibres deposited on the wire 13.

In each of FIGS. 4-13 inclusive it is assumed that the machine direction is vertical. As indicated in FIG. 4, fibres will lie at all angles 6 between and 90. If a fibre 31 lies along a direction which is at an angle 0 of less than 45 to the machine direction (FIG. 5) it imparts to the paper a strength component (cos 6) in the machine direction which is greater than the component (sin 0) in the crosswise direction. If a fibre 32 lies at a greater-than-45" angle (FIG. 6), the'reverse is true. In papers whose productionhas involved no special control of fibre orientation more than half the fibres lie along directions for which 0 is less than 45, and as a result the strength characteristics of the paper are as represented in FIG. 7. In this figure (and also-in FIGS. 8l3) illustrative vectors show by their varying lengths the relative tensile strengths of the paper in various directions. Thus, in FIG. 7, it is to be noted that the strength in the machine direction (vector 33) is greater than that in the transverse direction (vector 34). t i

In a square sheet or web, the strength characteristics are as shown in FIG. 8 in which vector 35 in the machine direction is the same length as transverse vector 36. i

It should be understood that the vectors in FIGS. 713 are proportional to the summation of strength components in the vector direction. Thus, in FIG. 7, the vector 33 is proportional to the summation of all the cos 0 components contributed by the fibres of which the paper is made, and similarly the vector 34 is proportional to the summation of all the sin 6 components. Obviously, in a paper having the characteristics depicted in FIG. 7:

2 cos 0 2 sin 0 and in a square paper (FIG. 8):

2 cos 0:2 sinfl For a paper to have the special characteristics contemplated by this invention, the fibres must be deposited on the wire in a special manner. The apparatus shown in box 11 from one of the side walls 22 thereof and term inates short of the opposite side wall. The propeller 20 is mounted on the end of a horizontal rotatable shaft 23 which is journaled in a bearing 26 in the side wall 22. A variable speed motor 27 is provided for rotating the shaft. As the paper stock circulates the suspended fibres adjacent to the wire 13 move in a direction having a large component transverse to the longitudinal axis of the wire. As the fibres are deposited on the wire, a majority of them (such as those shown at 18) will come to rest along directions forming angles 0 greater than 45 to the machine direction. The magnitude of this majority or preponderance, as well as the magnitude of the mean value of 0, will depend upon the relative speeds of the circulating stock and the wire 13;

Where the paper is to be used in making tubes, such as sausage casings, with the tube axis in the machine direction, the mean value of 0 must be at least (about) 63 and preponderance of fibers establishing this mean value must be more than normal. The reason for this is shown in FIGS. 9-13.

In FIG. 13 a strength diagram is shown, of a paper in which the mean value of 0 is 90. A comparison of vectors 37 and 38 indicates that 2 sin 0 2 cos 9 i.e., the paper is stronger in the crosswise direction than in the machine direction, but the ratio 2 sin 0 73 cos 0 obviouslydoes not equal 2. On the other hand, FIG. 12

depicts a similar paper in which a greater preponderance of laterally oriented fibres increases the length of vector 37a and makes it twice as long as vector 38a. The paper of FIG. 12 is therefore admirably suitable for the tubular use contemplated by this invention; the paper of FIG. 13 is not well suited for the present purpose because in the tubular form (FIG. 14) the paper must have a tensile (hoop) strength in the transverse direction T (compare with FIG. 3) which is twice that in the machine direction M.

In FIGS. 9-11 strength diagrams are shown, of papers in which the fibres are so oriented that the mean value of 6 is about 63 in each case. Note that in FIG. 10, the

. vector 39 isabout twice the length of vector 40, where- ,as in, FIG. 9 the vector 39a is less than twice as long as vector 40a, and in FIG. 11 vector 39b is more than twice as long as vector 4012. These difierent results stem from the different eccentricities of the ellipse-like loci of the vector ends. This eccentricity depends upon the degree of preponderance of the fibres establishing the mean value of 9. Papers having the strength characteristics of FIGS. 9 and 11 are not as well suited for the present purpose as a paper having the characteristics of FIG. 10.

Since the tangent of any angle less than (about) 63 is less'than 2, the desired strength characteristics cannot be attained if the means value of 0 is less than are tan 2.

Referring again to FIGS. 1 and 2, it has been found that where the wire 13 is given a speed of about feet per minute, and the speed of the propeller 20 is adjusted to give the paper stock a peripheral rotational speed (ad- .jacent to the wire) in excess of about 250 feet per minute, the paper produced has a transverse strength of 2390 grams per inch and. a longitudinal strength of 1240 grams per inch. This is almost the optimum strength ratio.

Similarly results were obtained at other wire speeds. fWith a wire speed of only 80 feet per minute, and with the slurry rotating at a speed that causes the fibers impinging upon the wire to have a peripheral speed of about -180 feet per minute, the strength ratio of the paper (transverse direction to machine direction) was 2.1 to 1.0. When the speed of the wire was increased to 150 feet per minute and the peripheral speed of the paper stock to the range of 310 to 330 feet per minute, the resultant paper manifested a strength ratio of 2.04 to 1.0. A ratio of 1.94 to.1.0 was attained when the wire speed was feet per minute and the stock speed between 370 and 385 feet per minute; and a strength ratio of 1.9 to 1.0 was found to exist in a paper made on a wire traveling 220 feet per minute with the peripheral speed of the stock impinging upon the wire between 450 and 475 feet per minute.

The web of paper 19 (FIG. 3) can be formed into a tube 28 (FIG. 14) by any known procedure or apparatus, and its lateral edges can be joined in any desired manner along a seam 29. If the tube is to be a sausage casing, the paper is preferably one whose fibres have been 'beaten only lightly if at all, and which is subsequently impregnated and treated in a special way. For example, viscose (cellulose xanthate) may be introduced into the interstices and then subjected to an acid bath whereby the cellulose is regenerated in situ. As a result, the paper serves as a kind of skeletal carrier for the regenerated cellulose. For other tubular purposes, special impregnation of this kind may not be required.

7 The cross-machine or transverse strength of the paper could of course be increased by increasing the general strength level of the paper by means of additional heating, a technique well known in the paper-making art. However, this does not achieve any change in the ratio of transverse strength to longitudinal strength, and it results in a reduction in porosity and absorbency, which would detract badly from the utility of the paper where it is to be subsequently saturated, as in the case of sausage casing tubing.

It will thus be seen that a continuous web of paper can be produced by this invention in commercial quantities and at low cost, in which the orientation of the fibres is such that the tensile strength of the paper in a crosswise direction is two times the strength in the machine direction, thus admirably qualifying the paper for use in a continuous fashion in the manufacture of a succ-ession of tubes having their axes parallel to the machine direction, the tubes having strength characteristics not heretofore attainable by commercially available paper except by piece-by-piece employment of severed sections.

In referring herein, and in the appended claims, to a ratio of 2 to 1 between transverse and longitudinal strengths, it is to be understood that precision may not be uniformly attainable in practice, and therefore reference to this ratio is intended to include within its scope not only the exact value 2 but also close approximations to it.

It will be understood that some of the details herein described and illustrated may be modified by those skilled in the art, without necessarily departing from the spirit and scope of the invention as expressed in the appended claims.

What is claimed is:

1. A method of forming a continuous web of paper suitable for formation into a tube, comprising the steps of supplying a paper fiber slurry to the headbox of an inclined wire Fourdrinier machine, rotating the slurry within the headbox so as to cause the fibers impinging upon the wire to have a major component of motion transverse to the longitudinal direction of the wire, and coordinating the speed of the wire and the rotational speed of the slurry so that the fibers are deposited on the Wire in an orientation predominantly in a direction about 63 to said longitudinal direction, the speed of the wire being between and 200 feet per minute, and the speed of the fibers impinging upon the wire being a little more than twice the speed of the wire.

2. A continuous web of paper, produced by the method set forth in claim 1.

3. The procedure defined in claim 1, in which the fibers are only lightly beaten before introduction into the headbox.

4. A continuous web of paper, produced by the method set forth in claim 3.

5. A continuous web of paper produced by the method set forth in claim 3 and subsequently treated to produce regenerated cellulose in its interstices.

References Cited by the Examiner UNITED STATES PATENTS 847,857 3/07 Walker et al 162-235 2,115,607 4/38 Becker 99-176 2,3 19,133 5/43 Hornbostel 162-235 FOREIGN PATENTS 328,992 11/20 Germany.

DONALL H. SYLVESTER, Primary Examiner. 

1. A METHOD OF FORMING A CONTINUOUS WEB OF PAPER SUITABLE FOR FORMATION INTO A TUBE, COMPRISING THE STEPS OF SUPPLYING A PAPER FIBER SLURRY TO THE HEADBOX OF AN INCLINED WIRE FOURDRINIER MACHINE, ROTATING THE SLURRY WITHIN THE HEADBOX SO AS TO CAUSE THE FIBERS IMPINGING UPON THE WIRE TO HAVE A MAJOR COMPONENT OF MOTION TRANSVERSE TO THE LONGITUDINAL DIRECTION OF THE WIRE, AND COORDINATING THE SPEED OF THE WIRE AND THE ROTATIONAL SPEED OF TH SLURRY SO THAT THE FIBERS ARE DEPOSITED ON THE WIRE IN AN ORIENTATION PREDOMINANTLY IN A DIRECTION ABOUT 63* TO SAID LONGITUDINAL DIRCTION, THE SPEED OF THE WIRE BEING BETWEEN 80 AND 200 FEET PER MINUTE, AND THE SPEED OF THE FIBERS IMPINGING UPON THE WIRE BEING A LITTLE MORE THAN TWICE THE SPEED OF THE WIRE. 